In a gas turbine engine, the combustion chamber receives air from the compressor, some of which air is mixed with the fuel which is burnt in the primary combustion zone. Ignition is performed by one or two igniter plugs situated downstream of the carburetion system. Another proportion of the air bypasses the primary combustion zone and mixes with the combustion gases. All of the hot gases are then directed toward the turbine. The combustion chambers are designed to meet a certain number of essential specifications such as: in-flight re-ignition, the shape of the temperature profile, the emissions of pollutant gases and the thermal and mechanical integrity of the various components thereof.
In particular, the ignition system has to ensure in-flight re-ignition in the event that the combustion chamber is accidentally extinguished, while at the same time withstanding and resisting the thermal stresses to which is subjected. These two conditions entail arrangements that are difficult to reconcile. Specifically, the injection system produces a sheet of atomized fuel that makes a certain angle. If this angle is a very tight angle then the igniter plug is outside of the cone formed by the fuel; this is preferable from a thermal integrity standpoint but the chamber ignition capability is poor. Conversely, an injection system in which the sheet of fuel forms a very wide cone causes significant heating of that zone of the chamber that surrounds the igniter plug, because of fuel impinging on the walls and the igniter plug. This adversely affects the thermal integrity of those elements.
The present invention relates to ignition systems in which the igniter plug is mounted on the chamber via a part that forms an adapter and is itself attached to the casing of the chamber. The igniter plug extends from the casing radially toward the inside of the chamber and its end lies flush with the wall of the chamber through an opening made therein and that forms a hollow shaft. A minimum lateral clearance is formed around the igniter plug to allow relative movements between the chamber and the casing as a result of temperature variations during the various phases of flight without the igniter plug, that secured to the casing, colliding with or pressing against the edges of the opening in the wall of the chamber. The opening in the wall of the chamber forms a hollow shaft into which the igniter plug is slid and a floating igniter plug sleeve surrounding the igniter plug provides sealing between the chamber and the space between the latter and the casing. One example of this way of mounting an igniter plug in a combustion chamber using an adapter is disclosed in patent application EP 1.443.190.
An igniter the end of which protrudes too far into the combustion chamber is exposed to thermal problems. These thermal problems carry the risk of causing incorrect operation of the engine and, above all, of causing the igniter plug to be destroyed more quickly. On the other hand, if an igniter plug is set back too far from the wall of the chamber, ignition performance is degraded. Hence the need to optimize the extent to which the end of the igniter plug is immersed with respect to the wall.
The state of the art means that the axis of the igniter plug always remains perpendicular to the axis of the chamber and there is therefore no ability of the igniter plug to compensate for axial and radial expansion of the chamber.